The invention relates to a system for indicating the cooling rate of a weld bead so that an operator can adjust a welding machine to insure that the cooling rate is within an acceptable range for obtaining a high strength and tough weld.
It is well known that when metal is cooled quickly, such as by quenching, desired mechanical properties may be obtained. Many metals are purposely cooled at a predetermined cooling rate so that they have a desired strength and toughness. While in many applications this is easy to achieve, it becomes somewhat difficult in welding operations. This is because a welding operation is a dynamic adventure where the cooling rate depends upon many variables including the travel speed of the torch, the voltage and amperage outputs of the welding machine and the preheat of the plate. If the torch is moved faster, while the voltage and amperage are kept constant, the cooling rate will rise, and if the torch is moved slower the cooling rate will drop. For any weld bead there is a desired cooling rate in order to achieve desired properties of strength and toughness. In the past the operator has relied upon preset parameters to achieve the proper travel speed of the torch. This is true with the ordinary in field welding machine as well as the more sophisticated gas metal arc welding machine wherein the torch is mechanically moved by the machine according to a travel speed set by the operator. Such a welding machine also includes adjustments for voltage and/or amperage to the torch. It is usually this kind of system where the rate of cooling of the weld bead becomes important because of their use in production lines where specific mechanical properties are desirable. If the operator could be provided with an indication of the rate of cooling of the weld bead he could then adjust the welding machine to provide an optimized weld.